1. Field of the Invention
The present invention relates to an endoscopic apparatus which is equpped with solid state image pickup elements on the tip of its scope.
2. Description of the Prior Art
In an endoscopic apparatus of the above kind, it is general to adjust the white balance by means of an electronic circuit, in view of the nonuniformity that may exist among individual apparatus in such items as the light source, light guiding fiber, lens, or their combinations, color filter that is mounted in front of the solid state image pickup element, spectroscopic sensitivity characteristic of the solid state image pickup element, or the like.
Further, although an apparatus of field sequential system does not employ a color filter, it instead makes use of three color filters that are placed on the light source side, and the nonuniformity of these filters needs be considered, so that it is also general to adjust the white balance by the use of an electronic circuit.
As the means of adjusting the white balance, it is general for television cameras to use two kinds of means. First one is means of manual type whose block diagram is shown in FIG. 1. Second means is of automatic type whose block diagram is shown in FIG. 2. The white balance is carried out in general by fixing green out of the three primary colors and regulating the amplitude of red (referred to as R hereinafter) and blue (referred to as B hereinafter) signals. Since, however, both of the means shown in FIG. 1 and FIG. 2 employ the same regulation method for R and B, only one system of block diagram is illustrated in these figures.
In FIG. 1, a gain regulation circuit 22 determines the amplitude of a color signal by regulating the gain of the circuit through manual variation of the volume. The color signal whose amplitude is regulated inthe above manner is input to a color difference circuit 23 in the next stage where the difference between the luminance signal (referred to as Y signal hereinafter) is taken as a color difference signal which is input to an encoder (Not shown. It is a circuit which generates a TV signal from the luminous the color difference signal and Y signal.). When the output amplitude of the gain regulation circuit 22 becomes small, the R signal, for example, tends to have a bluish-greenish hue and the B signal tends to have a yellowish hue. On the contrary, when the output amplitude of the gain regulation circuit 22 becomes large, the R signal tends to have a reddish hue and the B signal tends to have a bluish hue.
The means shown in FIG. 2 is of a system which automatically carries out the gain regulation. In the figure, there are provided an electronic attenuator 24 and a color difference circuit 25 that correspond to the gain regulation circuit 22 and the color difference circuit 23 in FIG. 1. The output of the color difference circuit 25 is input to a level clamp 26 whre DC regeneration is carried out for the purpose of comparison with a reference voltage in the next stage, and a black level (state of no signal) is set. A comparator 27 compares the output of the level clamp 26 and the reference voltage, and brings UP/DOWN a counter 28 in the next stage in accordance with the size of the signal. A D/A conversion circuit 29 converts the output from the counter 28 to an analog signal. The analog signal thus converted is input to the electronic attenuator 24 to vary its gain. As a result, the output of the color difference signal 25, too, is varied in response to the output of the D/A converter 29. This series of operation is set to work as the so-called negative feedback so that the color difference signals (R-Y and B-Y) are kept at constant values irrespective of the amplitude of the signal input.
In such white balance regulation means itself there is no special problem. However, there does exist a problem in the endoscope in that colors appear localized depending upon the area of the object. Thus, for instance, stomach presents a reddish hue overall, missing various other colors that are included in the scenery and indoor images. For that reason, when a white body, for instance, is seen in the interior of the stomach there is a problem that it appears somewhat reddish because of the light reflected from the wall of the stomach. In order to resolve such a problem, it is conceivable to perform a white balancing by placing a white body on the tip of the endoscope. However, this method is neither practical nor useful for accomplishing the white balance of the solid state pickup elements which has an inherent characteristic.
In addition, in diagnosis, a maximum information amount may not necessarily be guaranteed to be obtainable in a state in which the white balance is being kept. In fact, depending upon the nature of the disease there may be cases in which the conditions of the disease is more readily observable by toning down the level of red color or enhancing the level of blue color.